Can't edit Menu block on Entire Site

I have one menu block on the home page and another on Entire Site. Currently I cannot edit the Menu block on the entire site, but can successfully on the home page.
The behavior on Entire Site is that the block is red. I can open it and add a link, and put the link in the right lineup, but save is not possible. I have to just exit the endeavor.

What is the fix for this?

Now that I look at this, is part of the problem that the right side red of Entire site is broken in and of itself? Rather than this being a Menu block problem? I have no idea what to do

Update: The RED wasn't an indicator of an error. That section is supposed to be red just like another section is green. The reason I couldn't add a link to the menu block is because down in all the links, one of them was broken. Nothing would reveal that except manually clicking each link and checking it. I have no idea why it would have broken since I haden't changed any links in months (probably years). But I did find the broken link, fixed it, and then could add a new link and save the menu block. Thanks to Smugmug Help.